Mayyas, F., Fayers, P., Kaasa, S., & Dale, O. (2010). A systematic review of oxymorphone in the management of chronic pain. Journal of Pain and Symptom Management, 39(2), 296–308.

To assess the effectiveness of oxymorphone in the treatment of chronic pain

• Databases searched were MEDLINE, EMBASE, PubMed, and the Cochrane Central Register of Controlled Trials (CENTRAL).
• Search keywords were oxymorphone, oxymorphone ER, OPANA, oxycodone, randomized trial, randomized controlled study, pain, chronic pain, treatment, analgesia, human, cancer, back pain, and osteoarthritis. In addition, investigators performed manual searches based on reference lists.
• Studies were included in the review if they included level 1 evidence.
• The search did not involve exclusion criteria.

The search retrieved nine studies. Authors chose six studies for analysis. Five of the chosen studies were appropriate for meta-analysis. Only one study involved chronic pain resulting from a malignancy. Investigators, using guidelines published by the National Health Service Centre for Reviews and Dissemination, evaluated allocation procedures, concealment of allocation, blinding procedures,  distribution of known confounders between groups, whether study groups were treated the same except for the intervention, and whether intention-to-treat analysis was performed. Two reviewers independently reviewed and assessed all studies.

• The sample for analysis was composed of 1,426 patients. The sample range was 42–467 patients. Investigators analyzed data from 42 patients who experienced pain related to malignancies.
• The sample included adult patients with chronic low-back pain and pain related to osteoarthritis and cancer. The sample included opioid-naive patients and those who were taking opioids.
• Excluded from the study of cancer pain were patients who had undergone radiotherapy within the last two weeks.

In this study, oxymorphone 40–100 mg was associated with a significant reduction in the pain intensity experienced by patients with chronic pain unrelated to a malignancy. Total mean difference across studies was –12.88 (CI –17.08 through –8.68, p < 0.00001). Studies in which doses were titrated rather than fixed showed greater effect size. Adverse events were mild to moderate and similar to those associated with other opioids. The study of pain associated with malignancy, though small, demonstrated that oxymorphone was effective in the treatment of cancer pain and that switching between oxymorphone and oxycodone was feasible.

Findings suggest that oxymorphone is effective in chronic pain management. Note that the conversion ratio, oxymorphone to oxycodone, was 1:2.

Authors noted the high discontinuation rates in placebo groups; the high rates relate to the fact that some studies do not allow use of rescue medication. This fact has important implications regarding the design of studies in the field of pain management. Authors noted that regulators mandate placebo-controlled trials, and the authors highlighted the ethical concerns that such a requirement raises. In addition, authors noted the lack of placebo-controlled studies of patients with cancer pain.